1. Field of the Invention
This invention relates to a positioning apparatus which is used for projection exposure apparatuses used in semiconductor lithography, various kinds of precision processing machines, various kinds of precision measuring apparatuses, or the like.
2. Description of the Related Art
In projection exposure apparatuses used in semiconductor lithography, various kinds of precision processing machines, various kinds of precision measuring apparatuses, or the like, positioning of a substrate to be exposed, such as a wafer or the like, an object to be processed or an object to be measured with high precision, is required. In addition, recently, high-speed positioning is desired in order to improve the throughput of the operation.
FIGS. 8 and 9 are a plan view and a cross-sectional view, respectively, of a conventional top stage for performing focusing or final fine positioning of a substrate, such as a wafer or the like, with respect to a projection lens system in a projection exposure apparatus. Top stage E.sub.0 includes a circular holding board 104 having a suction surface (not shown) for attracting a substrate, such as a wafer or the like, by a vacuum suction force or the like. Holding board 104 is supported by a plurality of first piezoelectric elements 105 on top plate 101 of an XY stage (not shown). One end of each of the first piezoelectric elements 105 is elastically connected to annular member 103 adjacent to the outer circumference of holding board 104 via an elastic hinge 105a. Another end of each of the first piezoelectric elements 105 is elastically connected to top plate 101 via an elastic hinge 105b. Holding board 104 and annular member 103 are elastically connected by a plurality of first leaf springs 103a. A plurality of supporting members 102 provided as one body with top plate 101 and the outer circumference of annular member 103 are elastically connected by a plurality of second leaf springs 103b.
First piezoelectric elements 105 expand and contract by driving currents individually supplied to the respective elements, so as to bring holding board 104 away from and closer to top plate 101, and to change the relative angle of inclination between holding board 104 and top plate 101. Holding board 104 has a protruding arm 104a extending in the direction of its diameter through an opening 103c of annular member 103. A second piezoelectric element 106 is provided between the protruding arm 104a and a protruding arm 103d provided on annular member 103. Holding board 104 and annular member 103 retatively rotate by the expansion and contraction of piezoelectric element 106.
That is, by driving all of the first piezoelectric elements 105 by the same amount, holding board 104 is reciprocated about an axis perpendicular to the surface of top plate 101 (hereinafter termed a "z axis"), and by individually changing the driving amount for each of the first piezoelectric elements 105, the angle of inclination of holding board 104 with respect to the plane perpendicular to the z axis, i.e., the parallelism of holding board 104, is adjusted. Furthermore, by driving the second piezoelectric element 106, the angle of rotation of holding board 104 around the z axis is adjusted. Focusing and final positioning of a wafer (not shown) held on holding board 104 are performed by such fine adjustment.
However, in the above-described conventional approach, since the second piezoelectric element is connected to the annular member, which is moved by the first piezoelectric elements, a large amount of unbalance is produced in the mass of the annular member. In addition, oscillations generated when simultaneously driving the first and second piezoelectric elements mutually influence the stability of those elements, thereby causing a great decrease in dynamic characteristics as well as a decrease in the positioning accuracy. Accordingly, the speed of positioning using the top stage cannot be increased.
Furthermore, since the annular member and the holding board, and the supporting members, provided as one body with the top plate, and the annular member are connected by leaf springs, the annular member and/or the supporting members may deform by the reaction of the leaf springs when the amount of driving of each of the piezoelectric elements is large, thereby causing a decrease in the positioning accuracy.